Treating solution for planographic printing plates made with electrophotographic recording papers



United States Patent O 3,522,062 TREATING SOLUTION FOR PLANOGRAPHICPRINTING PLATES MADE WITH ELECTRO- PHOTOGRAPHIC RECORDING PAPERS SakaeShimizu, Kawasaki-shi, and Takayoshi Tanno, Tokyo, Japan, assignors toKabushiki Kaisha Ricoh, Tokyo, Japan, a corporation of Japan No Drawing.Filed Mar. 25, 1968, Ser. No. 715,563 Int. Cl. C09k 3/10 U.S. Cl. 106-23 Claims ABSTRACT OF THE DISCLOSURE A treating solution for planographicprinting plates made with electrophotographic recording papers, saidsolution comprising an aqueous solution containing a cyanide selectedfrom the group consisting of ferricyanides and ferrocyanides, at least aphosphate, and an organic polybasic acid containing at least twocarboxyl radicals, the total concentration of said phosphate and saidcyanide contained in said aqueous solution being at least 10% by weightof said solution, the proportion of said cyanide to said phosphatecontained in said solution being such that the total cyanide containedin these two salts is in the range of from 5% to 60% by weight of thetotal of these salts, the pH of said solution being controlled to avalue ranging from 3.0 to 7.0 by the addition thereto of said organicpolybasic acid.

BACKGROUND OF THE INVENTION Field of the invention The present inventionis concerned with a treating solution which is used in makinghydrophilic or oilrepellent the non-image areas of anelectrophotographic recording paper carrying a copied image producedaccording to a known electrophotographic copying procedure and intendedfor use as a planographic printing plate. The term treating solutionherein referred to includes also the fountain solution for use inplanographic printing, which is obtained by directly diluting saidtreating solution with water.

Description of the prior art There have been proposed in the pastvarious different compositions for the solutions intended for thetreatment of the printing faces of printing plates. However, no treatingsolution which is satisfactorily applicable to planographic printingplates made with electrophotographic recording papers (hereinafter to bereferred to briefly as recording papers) has as yet been reported.

These conventional treating solutions have a number of drawbacks incommon. To point out some of them, there are:

(1) They lack sufficient ability for making the printing face of theprinting plate oil-repellent, so that the prints will be susceptible tohaving the background stained with the printing ink during the processof printing;

(2) They are liable to develop cracks in the photoconductive layers ofthe recording papers during the treatment therewith; and

(3) The treating solutions of the prior art tended to infiltrate,through the aforesaid cracks in the photoconductive layers, into thesupport sheets of the recording papers, leading to a reduction in themechanical strength of the support sheets and resulting in thedevelopment of wrinkles in the support sheets. These drawbacks of thetreating solutions of the prior art appear markedly especially in theoffset printing which is performed on a small offset printing machinewith Simfio inking system.

SUMMARY OF THE INVENTION The present invention has been made afterextensive research conducted by us to overcome the aforesaid drawbacksof the treating solutions of the prior art from an overall viewpointwith respect to both the adaptability of the treating solutions to thefaces of the printing plates and the adaptability of the same to theprinting operation. More specifically, the treating solution of thepresent invention contains, as its principal components, a cyanideselected from the group consisting of ferrocyanides and ferricyanides, asalt of phosphoric acid and an organic polybasic acid containing atleast two carboxyl radicals (-COOH) in each of the molecules. Thepresent invention is further characterized in that the mixing ratio offerrocyanide or ferricyanide to phosphate in said treating solution, theconcentration of the cyanide and the phosphate, and the pH of thetreating solution, are all defined within predetermined ranges,respectively. The present in vention has its object in the provision ofa satisfactory planographic printing plate capable of exhibiting anexcellent printing eifect, by making the non-image areas of theaforesaid recording paper oil-repellent without the accompaniment of anysuch undesirable damages of the printing plate as those enumeratedabove.

The following are the essential and indispensable requirements of thepresent invention, namely, (1) that the mixing ratio of ferricyanide orferrocyanide to phosphate is such that the amount of said cyanidepresent in the total of said phosphate and said cyanide is in the rangeof from 5% to 60% by weight of said total of these salts, (2) that thetotal concentration of the cyanide and the phosphate in the treatingsolution is at least 10% by weight of said treating solution, and (3)that the pH of said treating solution is controlled to a value rangingfrom 3.0 to 7.0 by the inclusion of said organic polybasic acid.

As the ferrocyanides which can be applied to the present invention, theemployment of such cyanides as sodium ferrocyanide, namely, Na [Fe(SN)and potassium ferrocyanide, namely, K [Fe(CN) is desirable. As theferricyanides which are applicable to the present invention, theemployment of such cyanides as sodium ferricyanide, namely, Na [Fe(CN)and potassium ferricyanide, namely, K [Fe(CN) is desirable. As thephosphates which can be used in the present invention, there can beenumerated ammonium dihydrogen phosphate, namely, NH H PO diammoniumhydrogen phosphate, namely, (NH HPO sodium dihydrogen phosphate, namely,NaH PO and disodium hydrogen phosphate, namely, Na HPO As the organicpolybasic acids which are applicable to the present invention, there canbe used those organic acids having at least two carboxyl radicals whichinclude dibasic acids such as oxalic acid, malonic acid, succinic acidand adipic acid; unsaturated dibasic acids such as maleic acid anditaconic acid; and polybasic hydroxy-acids such as tartaric acid andcitric acid.

It is to be noted that by diluting one part of the treating solution ofthe present invention into several parts with water, the resultingdiluted treating solution can be utilized as the fountain solution foruse in planographic printing.

In case a planographic printing is performed while making oil-repellentthe non-image areas of the recording paper carrying a copied imageformed thereon according to a known electrophotographic copyingtechnique by the application thereto of the treating solution of thepresent invention and while using the fountain solution prepared bydiluting one part of said treating solution into the order of five partswith water, there are provided the advantages that all of the aforesaiddrawbacks inherent to the conventional treating solutions are greatlyim- 3 proved and that the fear of the occurrence of those t-roubles suchas the staining of the backgrounds of the prints, the staining of theprints due to the cracks developing in the photoconductive layers of therecording papers or due to the development of wrinkles in the supportsheets are completely eliminated.

While no theoretical explanation has been made yet as to the function ofthe ferrocyanides or ferricyanides, the phosphates and the polybasicacidswhich are the fundamental components of the treating solution ofthe present invention-to make the non-image areas of the recordingpapers oil-repellent, it has been observed by us that the Zinc oxidecontained in the photoconductive layer of the recording paper is causedto react upon these aforesaid components when they are placed in anacidic state, thereby producing an organic acid salt of zinc,ferrocyanide of zinc and zinc phosphates-such as Zn [Fe(CN) NH Z11PO andZn (PO )in the form of an oil-repellent film covering the surface of thenonimage areas of the photoconductive layer. It has been confirmed fromexperiments, however, that in case the mixing ratio of a ferrocyanide ora ferricyanide to a phosphate is such that the amount of the cyanidewith respect to the total of these salts exceeds 60% by weight, theresulting treating solution will be liable to develop changes due toexposure to light and due to temperature, and that thereby the abilityof the treating solution to make the non-image areas of the printingplate oil-repellent is reduced. On the other hand, in case theconcentration of the salts, namely, the cyanide and the phosphate, dropsto a level below not only there will arise an economical disadvantagethat the percentage of the dilution of the treating solutionwhen it isintended to prepare a fountain solution for use in planographic printingfrom said treating solution-will inevitably become small, but also therewill be apt to occur troubles in the process of printing due to theresulting excessively low concentration of these salts contained in thefountain solution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 Anelectrophotographic recording paper prepared with a specificallyprocessed strongly built support paper sheet provided on one surfacethereof with a photoconductive layer of about in thickness consisting ofa mixture of a zinc oxide and a silicone resin or a zinc oxide and asilicone plus styrenated alkyd resin which is prepared in the form thatzinc oxide is dispersed in the resin, was

used. This recording paper was then charged with electricity accordingto a known manner by the use of an ordinary electrophotographic copyingapparatus. Thereafter, the recording paper was exposed to light throughan original placed thereon, and the same was developed. Afterheat-fixation of the same, a copied image was obtained.

Then, the image-carrying face of said recording paper was wiped with apiece of absorbent cotton impregnated with a treating solution havingthe following composition, to thereby make the non-image areas of therecording paper oil-repellent, with the result that the recording paperbecame capable of use as a planographic printing plate. The compositionof the treating solution was as follows:

K Fe(CN) 5 Na HPO 5 NaH PO 5 Water 85 (The pH of the treating solutionwas controlled to 5.0 by the addition of citric acid).

The planographic printing plate having been given this oil-repellingtreatment was then applied to a planographic printing press. Printingwas performed by using a fountain solution which was prepared bydiluting one part of the aforesaid treating solution with 5 to 6 partsof water. Thus, more than 3000 clear prints were obtained withstability. There was noted no prints in which the non-image areas werestained with the printing ink or stained due to cracks occurring in theprinting face or due to wrinkles of the support paper.

In order to compare the ability of the treating solution of the instantexample with a conventional one, there was prepared a control treatingsolution having the following composition:

Weight percent Potassium ferrocyanide 2.0 Polyacrylic acid 1.5 Water,proper volume (The pH of the treating solution was controlled to 5.0 bythe addition of trisodium phosphate.)

In a manner similar to that described above, a planographic printingplate was prepared from a recording paper. When this printing plate wassubject to printing, there occurred cracks in the photoconductive layerof this control recording paper and also wrinkles in the support sheetat the end of about 2000 runs. It was noted that no further printingwould be possible. This result was confirmed by the comparativeexperiment of the abilities of these two treating solutions, which wasperformed repeatedly on several scores each of the recording papers ofboth.

Example 2 The non-image areas of the recording paper carrying an imagewhich was formed in the same manner as described in Example 1 were madeoil-repellent by using a treatment solution having the followingcomposition:

Na Fe(CN) 6 2 NaH PO 4 (NH HPO 6 Water 38 (The pH of this treatingsolution was controlled to 6.0 by the addition of succinic acid.)

As a result, a planographic printing plate was obtained. Then, afountain solution was prepared by diluting one part of this solutioninto 5 to 6 parts of water. Using this fountain solution, printing wasperformed in a manner similar to that described in Example 1. More than3000 clear prints were obtained without causing any trouble.

Example 3 A treating solution having the following composition wasprepared:

KgFe 6 1 NH H PO 3 Na HPO 5 Na-H2PO4 1 Water (The pH of this treatingsolution was controlled to 3.5 by the addition of adipic acid.)

This treating solution was used in the preparation of the planographicprinting plate and the preparation of a fountain solution. It was foundthat both the treating solution and the fountain solution made with thesame were of abilities which were substantialy equal to those ofExamples 1 and 2, permitting more than 3000 clear prints to be produced.

What is claimed is:

1. A solution for treating a planographic printing plate made of anelectrophotographic recording paper in order to render hydrophilic thenon-image areas of the plate without affecting the hydrophobic nature ofthe image areas, said recording paper being comprised of a support paperand a photoconductive layer formed on one surface of said paper, saidphotoconductive layer being comprised of a resin binder having suspendedtherein finely divided photoconductive zinc oxide, said solutionconsisting essentially of an aqueous solution of:

(a) a cyanide selected from the group consisting of alkali metal saltsof ferricyanides and ferrocyanides, (b) at least one water-solublephosphate selected from the group consisting of alkali metal andammonium salts of monoand di-hydrogen phosphate, and (c) an organic acidselected from the group consisting of oxalic acid, malonic acid,succinic acid, fadipic acid, maleic acid, itaconic acid, tartaric acidand citric acid; the ratio of said cyanide present in said solution tosaid phosphate present in said solution being such that the amount ofsaid cyanide is in the range of from 5% to 60% by weight of the totalamount of said cyanide and said phosphate, the pH of said solution beingcontrolled to a value ranging from 3.0 to 7.0 by the addition thereto ofsaid organic acid.

References Cited UNITED STATES PATENTS 10 2,988,988 6/1961 Kurz 101-4513,211,686 12/1965 Uber et a1. 101-451 XR 3,398,002 8/1968 Bondurant etal. 1062 JULIUS FROME, Primary Examiner 5 L. B. HAYES, AssistantExaminer US. Cl. X.R.

